(i) Discuss the extraction of copper from cuprous oxide or copper (I) oxide. (ii) What is the main difference between cupellation and poling? (iii) Why is it advantageous to roast a sulphide ore to the oxide before reduction?

(i) Discuss the extraction of copper from cuprous oxide or copper (I) oxide.
(ii) What is the main difference between cupellation and poling?
(iii) Why is it advantageous to roast a sulphide ore to the oxide before reduction?

Grade:Upto college level

1 Answers

Sunil Kumar FP
askIITians Faculty 183 Points
9 years ago

extraction of copper
(1)concentration of ore
Most copper ores contain only a small percentage of copper metal bound up within valuableoreminerals, with the remainder of the ore being unwanted rock organgueminerals, typicallysilicate mineralsor oxide minerals for which there is often no valueThe first stage of any process within a metallurgical treatment circuit is accurate grinding orcomminution, where the rock is crushed to produce small particles (<100 μm) consisting of individual mineral phases
(2)froth floatation process
removal of primary sulfide ore
The roasting process is generally undertaken in combination withreverberatory furnaces. In the roaster, the copper concentrate is partially oxidised to produce "calcine" andsulfur dioxidegas. Thestoichiometryof the reaction which occurs is:

2 CuFeS2+ 3 O2→ 2 FeO + 2 CuS + 2 SO2

The initial melting of the material to be smelted is usually referred to as thesmeltingormatte smeltingstage. It can be undertaken in a variety of furnaces, including the largely obsolete blast furnaces, reverberatory furnaces, flash furnaces, Isasmelt furnaces, etc.The product of this smelting stage is a mixture of copper, iron and sulfur that is enriched in copper, and which is calledmatteorcopper matte. The termmatte gradeis normally used to refer to the copper content of the matte.

The purpose of the matte smelting stage is to eliminate as much of the unwanted iron, sulfur andgangueminerals (such as silica, magnesia, alumina and limestone) as possible, while minimizing the loss of copper.This is achieved by reacting iron sulfides with oxygen (in air or oxygen enriched air) to produce iron oxides (mainly as FeO, but with some magnetite (Fe3O4)) and sulfur dioxide.

Copper sulfide and iron oxide can mix, but when sufficient silica is added, a separate slag layer is formed.Adding silica also reduces the melting point (or, more properly, theliquidustemperature) of the slag, meaning that the smelting process can be operated at a lower temperature.

The slag forming reaction is:

FeO + SiO2→ FeO.SiO2

Slag is less dense than matte, so it forms a layer that floats on top of the matt

The matte, which is produced in the smelter, contains 30–70% copper (depending on the process used and the operating philosophy of the smelter), primarily as copper sulfide, as well as iron sulfide. The sulfur is removed at high temperature as sulfur dioxide by blowing air through molten matte:

2 CuS + 3 O2→ 2 CuO + 2 SO2

CuS + O2→ Cu + SO2

In a parallel reaction the iron sulfide is converted to slag:

2 FeS + 3 O2→ 2 FeO + 2 SO2
2 FeO + SiO2→ Fe2SiO4

At theanode: Cu(s)→ Cu2+(aq)+ 2e–

At thecathode: Cu2+(aq)+ 2e–→ Cu(s)

Cupellationis arefining processinmetallurgy, whereoresoralloyedmetalsare treated under high temperatures and controlled operations to separatenoble metals, likegoldandsilver, frombase metalslikelead,copper,zinc,arsenic,antimonyorbismuth, present in the ore.The process is based on the principle thatprecious metalsdo notoxidiseor react chemically, unlike the base metals; so when they are heated at high temperatures, theprecious metalsremain apart and the others react formingslagsor other compounds

Polingis a method employed in the purification ofcopperwhich containscuprous oxideas an impurity. The impure metal, usually in the form of molten blister copper, is placed in an anode furnace for two stages of refining. In the first stage, sulfur and iron are removed by gently blowing air through the molten metal to form iron oxides and sulfur dioxide. The iron oxides are skimmed or poured off the top of the copper and the gaseous sulfur dioxide exits the furnace via the off-gas system. Once the firstoxidationstage is complete, the second stage (reductionorpoling) begins. This involves using a reducing agent, normally natural gas or diesel (but ammonia,iquid petroleum gas,and naphtha can also be used), to react with the oxygen in the copper to form copper oxide. In the past, freshly cut ("green") trees were used as wooden poles. The sap in these poles acted as the reducing agent. The heat of the copper makes the pole emit a gas that reduces the cuprous oxide to copper.

It was the use of these poles gave rise to the term "poling".

(3)preference of oxide to sulfide
Sulphide ores are invariably roasted to convert them to oxide and then reduced to
the metal. The roasting process also removes volatile impurities such as arsenic. For
thermodynamic reasons, an oxide rather than a sulphide is used for reduction.
Sometimes, the sulphides are oxidized to sulphate or some other soluble salt and the
metal obtained from it by chemical or electrolytic reduction.

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